2 MAI 2018
In 1973-74 a field party from the Directorate of Overseas Surveys’ (DOS), established trigonometrical control for a 1:50,000 scale photo-mapping of Lake Chad.
The team consisted of Henry Rogers (Oi/c), Duncan Shiell and David Latham-Ward and their locally recruited labour force.
Until then the only available mapping was at a scale of 1:200,000 which did not cover the entire lake, let alone the whole basin that stretches across Chad, Cameroon, Niger and Nigeria.
The Lake Chad Basin Commission, which had been set up in the 1960s, recruited DOS to carry out mapping of the lake area in support of an increasing number of development projects which needed detailed and up to date mapping. Due to the incredibly flat relief of the area, a contour map would have been meaningless to this project.
The field team were responsible for identifying and fixing the trigonometrical points on all of the aerial photographs. The scale and position of each individual photographic image was then determined by the slotted template assembly, ultimately allowing the photographic images to join together in a way that was dimensionally correct.
Whilst the fieldwork was a routine application of well-tried techniques, some of the production techniques used to present the photo-mapping information was considered innovative for its time. Given full colour digital photography cover had not yet been developed, the DOS were able to build a colour coded half tone image from the black and white aerial photography through a technique referred to as 'shadow-line’, a method that enhanced natural detail.
Lake Chad itself is very shallow and small changes in water levels make large differences to shorelines. Sadly, the lake has contracted a massive 95% between the years 1963 and 2001. The 1973 photo-maps conducted by the team have continued being of an importance, providing a useful comparison with current satellite imagery of the continuation of this climate change crisis.